1. Field of the Invention
The present invention relates to apparatus and methods for mariculture and more particularly to a salinity driven oceanographic upwelling.
2. Description of the Prior Art
Marine farming of mariculture products such as fish requires the presence of an adequate fertilizer. Ideally, the fertilizer should be available at the water surface to foster the development and growth of mariculture at the water surface and thereby facilitate the harvesting or retrieval of the mariculture.
A desirable fertilizer for fish mariculture includes inorganic materials such as phosphorus. Unfortunately phosphorus material is not present in surface water of the ocean, for example, in sufficient enough quantities to produce commercially viable maricultures. Therefore, in order to develop a mariculture farm in the ocean it is necessary to add the requisite amounts of fertilizer to the water surface at a desired location.
One known approach for providing fertilizer for a mariculture is to dump material containing the fertilizer into the water at a prescribed location suitably surrounded by a known barrier or border structure. However the collection, transportation and dispensation of fertilizer-laden material are usually too expensive to make mariculture farms commercially feasible.
In numerous oceanic locations around the world the water at depths greater than 100 meters is relatively fresh, colder and substantially nutrient rich in comparison with the surface water, which is warmer, has greater salinity and is nutrient deficient. The deep water is also denser than the surface water due to the difference in salinity at such water levels.
However, previous attempts to pump the nutrient-rich deep water to the surface have proven impractical because of the fuel costs for the pumping operation. Furthermore, the efficiency of such a pumping operation is also relatively low since the deep water, because of its high density, has a tendency to sink as soon as it is pumped to the ocean surface.
Another known method of bringing nutrient-rich deep water to the surface, is described in the article "An Oceanographical Curiosity; The Perpetual Salt Fountain" by H. Stommel, A. B. Arons and D. Blanchard, published in Deep Sea Research, Vol. 3 (1955), pages 152-155. The method includes placement of a long, vertical pipe into the ocean in such a manner that the bottom of the pipe is exposed to cold, relatively fresh water, while the top of the pipe is in warm saline water. A continuous flow of deep water up the pipe is expected to result after the fountain is primed supposedly due to an exchange of heat, but not salinity, with the ambient ocean. A further investigation of this salt fountain is made in the article "The Salt-Fountain and Thermohaline Convection" by M. E. Stern, published in Tellus, Vol. 12 (1960), pages 172-175.
The flow rates for a single pipe exchanging heat with the ambient ocean are estimated for pipes of various diameters in the article "Flow Estimates for the Perpetual Salt Fountains" by G. W. Groves, published in Deep Sea Research, Vol. 5 (1959), pages 209-214. According to this article, a pipe 600 meters long and having a 20 centimeter diameter, when installed at an angle that locates the bottom of the pipe 300 meters below the surface, might produce a flow rate of 5.5 liters per second. Presumably this upwelling would supply phosphorus to produce 54 kilograms per year of edible fish.
The same amount of phosphorus could be added to the water by using 290 kilograms per year of Peruvian guano, which has a phosphorus content of 4.6%. Thus the article by Groves concludes that the artificial upwelling is not feasible.
However, applicant has recognized the problem that the size of an artificial upwelling may determine the practicality of marine farming using an upwelling. It is proposed that a commercially viable mariculture should be conducted on a large scale, that is, much greater than 10 acres. There are also other products of a mariculture besides fish which may be commercially viable. These products would require other fertilizers besides phosphorus, such as nitrogen, which do not have cheap alternative sources. For example, kelp for use as a feedstock to produce synthetic natural gas has been proposed as a mariculture product and is fertilized with nitrogen.
Nitrogen is not present in sufficient quantities in surface water to provide a commercially viable kelp yield. A recent article entitled "Systems Analysis Studies on Marine Biomass Commercial Application" by Sullivan, McGinn, Jain and Engel, published by the General Electric Corporation, concluded that commercial nitrogen fertilizer would be too expensive for marifarming even if the only cost consideration was the energy requirements necessary to produce the nitrogen fertilizer.
Deep ocean water is typically rich in nitrogen. Thus the commercial viability of a kelp farm would depend on the development of an economical method for bringing deep water to the ocean surface.